ncl30051 ON Semiconductor, ncl30051 Datasheet - Page 11

• Manufacturer Part Number: ncl30051
• Description: Ncl30051 Product Preview Two Stage Pfc And Resonant Half Bridge Controller Combo For Led Lighting
• Manufacturer: ON Semiconductor

network. Equation 5 is used to calculate the values of the
PFC feedback network.
gain, gm. That is, the output current is controlled by the
differential input voltage. The NCL30051 amplifier has a
typical gm of 95 mS. The PControl pin provides access to the
amplifier output for compensation. The compensation
network is ground referenced allowing the PFC feedback
signal to be used to detect an overvoltage condition.
selected to filter the bulk voltage ripple such that a constant
control voltage is maintained across the ac line cycle. A
capacitor between the PControl pin and ground sets a pole.
A pole at or below 20 Hz is enough to filter the ripple
voltage for a 50 and 60 Hz system. The low frequency pole,
f
where, C
ground.
is that the input is allowed to move independently with
respect to the output, since the compensation capacitor is
connected to ground. This allows dual usage of the
feedback pin by the error amplifier and by the overvoltage
comparator.
PFC Undervoltage
pin is left open. An undervoltage detector disables the
controller if the voltage on the PFB pin is below
V
current source, I
if the PFB pin is floating. The PFB pull down current source
affects the PFC output voltage regulation setpoint.
PFC Overvoltage
voltage and disables the PFC driver if the PFC output voltage
is greater than 5% of its nominal value. PFC drive pulses are
suppressed until the overvoltage condition is removed. The
overvoltage detector tolerance is better than ±2% across the
operating temperature voltage range. The overvoltage
comparator hysteresis is typically 30 mV (1.2%).
PFC Overcurrent
detector. The PCS pin provides access to the overcurrent
detector. The PFC drive pulse is terminated if the voltage
on the PCS pin exceeds the overcurrent threshold,
V
basis. The overcurrent threshold is typically 0.84 V.
caused by the power switch transitions. The NCL30051 has
p
PUVP(low)
PCS(ILIM)
, of the system is calculated using Equation 6.
A transconductance amplifier has a voltage−to−current
The compensation network on the PControl pin is
A key feature to using a transconductance type amplifier,
The NCL30051 safely disables the controller if the PFB
An overvoltage detector monitors the PFC feedback
The PFC current is monitored by means of an overcurrent
The current sense signal is prone to leading edge spikes
PControl
V
. This comparison is done on a cycle by cycle
, typically 0.23 V. A 1.2 mA (typical) pull down
PFC
+ V
PFB
is the capacitor on the PControl pin to
, ensures V
PREF
f
p
+
@
2pC
R
1
R
) R
gm
PControl
PFB
2
2
falls below V
) I
PFB
@ R
1
PUVP(low)
http://onsemi.com
(eq. 5)
(eq. 6)
11
leading edge blanking circuitry that blocks out the first
110 ns (typical) of each current pulse.
PFC Driver
60 and 15 W, respectively. Depending on the external
MOSFET gate charge requirements, an external driver may
be needed to drive the PFC power switch. A driver as the
one shown in Figure 9 can be easily implemented.
Half−Bridge Driver
The oscillator frequency is divided by two before it is
applied to the half−bridge controller.
HDRVlo, and a 650 V high side driver, HDRVhi. The built
in high voltage driver eliminates the need for an external
transformer or dedicated driver. A built−in delay between
each drive transition eliminates the risk of cross
conduction. The delay is typically 785 ns. The typical duty
ratio of each half−bridge driver is 48%.
and the HVS pins as shown in Figure 10.
The PFC driver source and sink impedances are typically
The half−bridge stage operates at a fixed 50% duty ratio.
The half−bridge controller has a low side driver,
The high side driver is connected between the HBoost
Figure 10. Half−bridge High Side Driver
Figure 9. External Driver