SSL152x
SMPS ICs for mains LED drivers
Rev. 02 — 10 March 2009
Product data sheet
1. General description
The SSL152x family is a Switched Mode Power Supply (SMPS) controller IC that operates
directly from the rectified universal mains. It is implemented in the high-voltage
EZ-HV SOI process, combined with a low-voltage BiCMOS process. The device includes
a high-voltage power switch and a circuit for start-up directly from the rectified mains
voltage.
A dedicated circuit for valley switching is built in, which makes a very efficient slim-line
electronic concept for solid state lighting applications possible.
The SSL152x can operate in applications with a power range of up to 15 W. For a power
range between 15 W and 25 W the SSL1623PH is the best choice. For LED powers above
25 W the SSL1750 can be used.
In its most basic applications, the SSL152x family acts as a voltage source. Here, no
additional secondary electronics are required. A combined voltage and current source can
be realized with minimum costs for external components. Implementation of the SSL152x
family renders an efficient and low cost power supply system for mains LED drivers.
2. Features
I
Designed for mains LED drivers up to 15 W
I
Integrated power switch:
N
SSL1522T: 12
Ω;
650 V
N
SSL1523P: 6.5
Ω;
650 V
I
Operates from universal AC mains supplies (80 V to 276 V)
I
Adjustable frequency for flexible design
I
RC oscillator for load insensitive regulation loop constant
I
Valley switching for minimum switch-on loss
I
Low standby power (< 100 mW) with frequency reduction at low power outputs
I
Adjustable overcurrent protection
I
Undervoltage protection
I
Temperature protection
I
Short circuit winding protection
I
Simple application with both primary and secondary (opto) feedback
I
Available in DIP8 and SO14 packages
NXP Semiconductors
SSL152x
SMPS ICs for low power systems
8. Functional description
The SSL152x family is the heart of a compact flyback converter, with the IC placed at the
primary side. The auxiliary winding of the transformer can be used for indirect feedback to
control the isolated output. This additional winding also powers the IC. A more accurate
control of the output voltage and/or current can be implemented with an additional
secondary sensing circuit and opto coupler feedback.
The SSL152x family uses voltage mode control. The switching frequency is determined by
the maximum transformer demagnetizing time and the frequency of the oscillator. In the
first case, the converter operates in the Self Oscillating Power Supply (SOPS) mode. In
the latter case, it operates at a constant frequency, which can be adjusted with external
components R
RC
and C
RC
. Furthermore, a primary stroke is started only in a valley of the
secondary ringing. This can use constant power or constant current mode to drive LEDs.
The valley switching principle minimizes capacitive switch-on losses.
8.1 Start-up and undervoltage lockout
Initially, the IC is self-supplying from the rectified mains voltage. The IC starts switching as
soon as the voltage on pin V
CC
passes the V
CC(startup)
level. The supply is taken over by
the auxiliary winding of the transformer as soon as V
CC
is high enough and the supply
from the line is stopped for high efficiency operation.
When for some reason the auxiliary supply is not sufficient, the high-voltage supply also
supplies the IC. As soon as the voltage on pin V
CC
drops below the V
CC(stop)
level, the IC
stops switching and restarts from the rectified mains voltage.
8.2 Oscillator
The frequency of the oscillator is set by the external resistor and capacitor on pin RC. The
external capacitor is charged rapidly to the V
RC(max)
level and, starting from a new primary
stroke, it discharges to the V
RC(min)
level. Because the discharge is exponential, the
relative sensitivity of the duty factor to the regulation voltage at low duty factor is almost
equal to the sensitivity at high duty factors. This results in a more constant gain over the
duty factor range compared to systems with a linear sawtooth oscillator. Stable operation
at low duty factors is easily realized. For high efficiency, the frequency is reduced as soon
as the duty factor drops below its low power threshold. This is accomplished by increasing
the oscillator charge time.
To ensure that the capacitor can be charged within the charge time, the value of the
oscillator capacitor should be limited to approximately 1 nF.
8.3 Duty factor control
The duty factor is controlled by the internal regulation voltage and the oscillator signal on
pin RC. The internal regulation voltage is equal to the external regulation voltage (minus
2.5 V) multiplied by the gain of the error amplifier (typically 20 dB).
SSL152X_2
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 02 — 10 March 2009
5 of 17
Embedded System
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