Justin Kai EE 136 Project Prof. Zhou

1. Constant Current Power Supplies, Variable Linear Power supplies & Switchmode Variable Power Supplies Justin Kai EE 136 Project Prof. Zhou

2. Constant-Current Power Supplies

3. Important Parameters • Nominal operating voltage rage • Compliance voltage (upper limit) • Current limit

4. Nominal Operating Mode

5. Voltage Over-loaded Mode

6. Linear Variable Power Supply (Char.) • Low noise level (micro-volt. Range) • Fast full recovery time • High power dissipation (low efficiency)

7. Basic Drive Circuit “Piggyback”

8. Basic Operation Considerations • Low voltage, High current output Q2=off Volt. drop in R1 (high power dissipation) • High voltage, High current Q2=on short R1 (low power dissipation)

9. Power Loss Chart

10. Switchmode Variable Power Supply • SMV power supply are small, light & efficiency will be maintained near 70% • One SMV can replace up to Three Variable Linear power supplies • SMV power supplies are very noisy  need special kind of filters are required

11. Requirements of SMV Power Supply • Noise filtering must be optimum. Conventional filters cannot obtain the requirements in high accuracy applications • Faraday screen for switching sections and filters are essential, need metal or screened cabinets  minimize the EMI problems • Operating low output voltages demand very narrow power pulses • Basic supply with Fly-Back Converter transformer can be considered a constant energy source

12. Block Diagram of SMV Power Supply

13. Advantages: Low noise levels Fast full recovery Disadvantages: High power dissipation Large, heavy & inefficient Expensive heat sinks & transistors are required Advantages: small, light & efficient 1 SMV can replace 3 VL power supplies Disadvantages: SMV power supplies are very noisy  need special kind of filters are required Comparison (VL & SMV)