There’s great news for you if you are one of those looking for a DC-DC bias supply with small outputs that you can use for your projects. Brian Cornell, an electronic enthusiast with an interest in power management, has built a DC-DC bias power supply using Texas Instruments’ LM5xxx series IC.
Cornell oftentimes has kicked around the idea of designing one that has some configuration flexibility but this time he obviously did not want to spend the time since a 5W design can demand just as much time as a 500W.
The LM50xx family of regulators is non-isolated buck regulators known for a number of incredible features including simplicity, low-cost wide Vin range, and output configuration flexibility. Cornell started by adding extra windings to obtain outputs at different voltages which could be tied to the primary ground or isolated. He then used a constant on-time PWM scheme to eliminate the traditional compensation network required to close the control loop. The artifact of the constant on-time control scheme however showed the control loop requires some ripple for stability (a contributing factor is the small output capacitance) so he went ahead to add a small LC filter to the output to solve this problem.
Cornell, however, noted that the LM5017 has a current limit of 600mA which would not be enough to handle the power required of both outputs, but one can use the LM5161 which is a higher power sibling of LM5017 that integrates more features.
SPECIFICATIONS (As Configured)
- Vin 10.6 – 30V DC (tested to 25V)
- # Outputs – 2 (V1, V2)
- V1 – +5V, 300mA, 1.5W, non-isolated
- V2 – +12V, 200mA, 2.4W, [non]-isolated
- Output ripple: V1 < 10mV P-P, V2 < 20mV P-P
- Regulation: V1 – 1%, V2 – 11% (over Vin range, V1 & V2 @ full load)
- Transient response (3mS pulse, 20%->100% load)
V1 – 250uS
V2 – 960mV droop
- Peak efficiency: 84.5% (V_in=14V, V1 & V2 @ full load)
- Average efficiency: 83% (over Vin range, V1 & V2 @ full load)
- Low efficiency: 81.5% (Vin=10.6V, V1 & V2 @ full load)
- Radiated EMI: not tested
- Operating temperature: -40C (characterized) – +85C (tested)
- Soft start
- Protection: over current, thermal shutdown
- Dimensions(LWH): 4.7cm x 2.3cm x 1.6cm (1.85″ x 0.91″ x 0.63″)
- Unit cost: $23.00 (excluding assembly time & materials)