5.19 Efficiency Data

Table 5-9. Efficiency Data for V_IN = 800V, V_OUT = 12V
I_OUT Steps (A)	V_IN Measured (V)	I_IN Measured (A)	P_IN Calculated (W)	V_OUT Measured (V)	I_OUT Measured (A)	P_OUT calculated (W)	Efficiency (%)
5	800	0.13	104	12.05	5.1	61.5	59.09
20	800	0.38	300	12.05	20	241	80.33
35	800	0.59	472	12.05	35	421.8	89.35
50	800	0.82	652	12.04	50.1	603.2	92.52
65	800	1.05	840	12.02	65	781.3	93.01
80	800	1.28	1024	12.01	80.1	962.0	93.95
95	800	1.51	1208	12	95.1	1141.2	94.47
110	800	1.75	1396	12	110.1	1321.2	94.64
125	800	1.99	1588	12	125.1	1501.2	94.53
140	800	2.23	1780	12	140.1	1681.2	94.45
155	800	2.47	1976	11.99	155.1	1859.7	94.11

Table 5-10. Efficiency Data for V_IN = 470V, V_OUT = 12V
I_OUT Steps (A)	V_IN Measured (V)	I_IN Measured (A)	P_IN Calculated (W)	V_OUTMeasured (V)	I_OUT Measured (A)	P_OUT Calculated (W)	Efficiency (%)
5	470	0.19	89.3	12.05	5.1	61.46	68.82
20	470	0.6	282	12.05	20	241	85.46
35	470	0.96	451.2	12.05	35	421.75	93.47
50	470	1.35	632.15	12.03	50.1	602.70	95.34
65	470	1.74	817.8	12.03	65	781.95	95.62
80	470	2.14	1005.8	12.02	80.1	962.80	95.72
95	469.9	2.55	1195.77	12.01	95.1	1142.15	95.52
110	469.8	2.96	1388.26	12	110.1	1321.2	95.17

Table 5-11. Peak Efficiency Operating Point
I_OUT Steps (A)	V_IN Measured (V)	I_IN Measured (A)	P_IN Calculated (W)	V_OUTMeasured (V)	I_OUT Measured (A)	P_OUT Calculated (W)	Efficiency (%)
73	470	2.02	949.2	12.51	73.1	914.48	96.34

Peak efficiency was achieved at a lower voltage with significant current. This enables ZVS at a relatively lower output power. In this case, high ZVS was achieved at a low voltage of 470V and 915W output. A lower input voltage at a nominal output voltage results in greater duty cycle, reducing time of circulating current at primary PSFB. Lower output power at the nominal output voltage 12.51V means lower conduction losses at the secondary.

Figure 5-43. Measured Efficiency vs Output Power

At higher input voltage (i.e., 800V) for the same amount of output power, the peak transformer primary current is smaller compared to V_IN = 470V. This results in low ZVS and increases switching losses at primary side phase-shifted full-bridge. At Pout > 1000W, the efficiency starts to increase significantly due to higher ZVS and approaches maximum efficiency of 94.64% around nominal load.

The ZVS operating point may be changed by adjusting the leakage inductance at primary full-bridge.