0.5v Negative Supply 4 A while back someone needed a simple way to generate a negative 0.5v supply from a conventional transformer type AC to DC power supply.  The circuit below uses a couple schottky diodes and a filter capacitor to perform the feat.  The circuit is handy when using �rail to rail� op Amp circuits which get close to zero volts at their output from a single DC supply but can�t quite deliver without a negative supply.  With the aid of the 0.5v supply circuit shown, those devices can produce a true zero output voltage. [Circuit of the week designed by David Johnson]Request a Sample / Buy Now The Artesyn Embedded Technologies LCM1500 provides a low cost solution to Industrial and Medical single output high power requirements. Full featured, the 2.4" x 5" x 10" enclosed form factor utilizes a smart fan for self contained thermal management at very low acoustic noise levels. Digital DSP control allows for a high level of modification flexibility.

Voltage output for the series ranges from 10.8V - 52.8V at a continuous output power of 1500W. The LCM1500 also provides an optional 5V Standby and many optional I/O configurations Universal PMBus GUI Software Package 90 V to 264 V Output Voltage: 10.8 V to 52.8 V Size (L x W x H): 10.000" x 5.000" x 2.400" Hold-up Time: 20 mSec Power Factor: 0.99 Typical Inrush Currect: <= 25A Peake Frequency: 47 - 440 Hz Input Range: 90-264 VACautomotive air conditioning repair equipment Leakage: <0.3mA at 264 VAC Efficiency: >89% TYPac and heating school Over Voltage Protection: 125% to 145% of rated outputmy ac unit has ice Over Current Protection: 105% to 125% of rated output Current Share: Forced to within 10%

Max Units in Parallel: 10 Noise (P-P): 1% max Total Regulation: +/- 2.0% Adjust Range: +/- 10% Fan Noise: <45dBA, 80% load 30C, off with inhibit 1500W Output Power with no derating 12 Watts per cubic inch Latest CCC approvals (5000m) -40C to 70C with derating Optional 5V @ 2A Housekeeping High Efficiency: 89% typical Variable Speed Smart Fans Models - Stock Check Here's another take on the transformerless AC line power supply, which finds use in some well-insulated, low-power devices. Our technical reviewer pointed out that Cac should be an X-rated safety type, and I think we'd both feel better if the ground symbol wasn't there! SMPS circuits offer an efficient way to reduce AC from a mains source to any desired level for powering low-voltage circuits, though this comes at the cost of components such as control ICs, switching transistors, inductors, etc. Figure 1 shows a simple way you can use more common components to step-down and regulate the AC mains to the desired low DC voltage.

The reduction in AC voltage is obtained by dropping the unwanted extra voltage across a capacitor (impedance Z=1/ωC) Cac of suitable value and voltage rating. The remaining AC is drawn as rectified output through a diode bridge. So even though DC flows through the output circuit of the bridge, the voltage dropping series capacitor Cac sees an AC flowing in its remaining part of the circuit. The value of the capacitor determines the current output at reduced voltage. A larger capacitor is required for larger output currents. A bleeder resistor (1MΩ) is set in parallel with Cac to discharge it when the AC is disconnected. The DC after rectification and filtering is shunted by the Q1-based regulation circuit, which basically tries to maintain the output voltage within certain limits. 1 This step-down converter drops AC mains voltage across Cac to produce a lower DC voltage. is optional and is related to safety issues – choose higher wattage if is the unregulated output which can be further regulated using chips

like 7805/12 etc or a simple zener-transistor regulator. chosen according to power requirement – essentially it should be able to drain the unused current when the load is absent. of fuse are indicative – choose it according to your design/need. The circuit has two LEDs. The red LED indicates whether the power from AC is being used, or bled as waste through Q1. The green LED indicates the power availability at the output where further regulating devices can be added. R1, R2, and RB (R1,R2 » RB) form a voltage divider network which essentially monitors the residual rectified AC from the bridge. Their values are chosen such that when the current is flowing through the load (not shown), Q1 is switched off and hence little current flows through the second bleeder resistor RB, limited by the large values of R1 and R2. The voltage drop across RB is not sufficient to turn on the red LED. At this point, we say the current flowing through R1, R2, and RB is the housekeeping current which constantly flows apart from the maximum load current.

Q1 is biased by the voltage drop across R2, which should be at least 0.6V for Q1 to turn on. During normal operation (current flowing through the load), the values of R1, R2, and RB are chosen such that this voltage is less than 0.6V. However, if the load is disconnected (no output current is being drawn) then the voltage after the diode bridge will increase, which in turn will increase the voltage drop across R2 until the transistor turns on and draws current through RB. This stops the voltage from increasing further, simultaneously increasing the current through the red LED. A glowing red LED indicates power wastage. However, the green LED always glows when power is available at the output. RB should be chosen such that the rise in voltage at the bridge output during no load condition is within the upper limit of any final regulator connected to +VU. The required capacitor Cac is calculated as: where IL is the maximum load current, Vrms is the RMS AC voltage, VE (~VU+1.2) is the residual expected voltage at the bridge input, which is taken to be the sum of VU and 1.2V across the bridge diodes.

ΔIL is the house keeping current apart from the maximum load current. A rough estimate of Cac is IL / (ωVrms) (where ω = 2πfAC) as can be seen from the formula by neglecting ΔIL and VE, which are small compared to IL and Vrms respectively. This circuit offers an alternative to a bulky, noisy, vibration/magnetic field/heat producing transformer. However, the advantage of the transformer is in the isolation it offers from live AC. The danger with the proposed circuit is when Cac shorts out. Precautions should be taken to see that the fuse blows out before the voltage across the output rises to a hazardous level. Under increased voltage conditions, extra current paths are offered by the zener VUZ and the filter capacitor CF . Additional cheap neon lamps can be added across the bridge input to salvage the output regulating circuit and the load. In a test set up which was designed to obtain a zener-transistor regulated 4.8V supply at 5mA current: Cac=0.068μF, R1=10kΩ, R2=470Ω, RB=470Ω, CF=470μF, and Q1=BC549, with a 240V AC line.